Our car radio has the annoying habit of forgetting what part of a CD it was playing when you turn it off. On long drives this is a real drag; I’ll leave an audio book playing for my family in the car while I gas up, and when I turn the key from Accessory to Start, the radio turns off and back on again.

I built a cheap circuit that keeps the radio powered up five seconds after accessory power is interrupted, and this keeps the radio running while the engine turns over. The three key components for this circuit are a diode, a capacitor and a relay.Read more…